1. Field of the Invention
The present invention relates to a multi-beam scanning apparatus, and more specifically relates to a multi-beam scanning apparatus capable of changing resolution.
2. Description of the Related Art
Japanese Laid-Open Patent Application Nos. 57-54914 and 58-68016, for example, disclose the art to change resolution in a multi-beam scanning apparatus that forms an image on a scanned surface via a plurality of laser beams.
In the multi-beam scanning apparatus disclosed in Japanese Laid-Open Patent Application No. 58-68016, resolution is switched by providing components to change the advance direction of the luminous flux in an optical path before laser beams are overlaid, and changing the beam spacing in a subscan direction on a scanned surface via said components. In the multi-beam scanning apparatus disclosed in Japanese Laid-Open Patent Application No. 57-54914, resolution is switched by providing an afocal anamorphic zoom lens system to change the image forming magnification in a subscan direction, and changing the beam spacing in a subscan direction on a scanned surface via said zoom lens system.
In the multi-beam scanning apparatus of Japanese Laid-Open Patent Application No. 58-68016, a mechanism is required to switch the resolution before the laser beams are overlaid on the optical path. Therefore, disadvantages arise inasmuch as the number of components is increased and the optical system before the laser beams are overlaid is more complex, and maintaining the relative position accuracy of the beams becomes more difficult due to the increase in relative displacement error of the beam positions resulting from said increased complexity. A further disadvantage arises in increased cost associated with, for example, the requirement for a relative position adjustment mechanism via feedback control.
Consider a method which uses a light source to generate a plurality of laser beams rather than overlaying laser beams to form a plurality of light sources as one method of realizing image formation via a plurality of laser beams. In this instance, the light emission point spacing must be on the order of several microns to have the convergence position spacing on the scanned surface of either 1 dot or several dots. Each laser beam must be quickly overlaid directly after the light source. Therefore, the art proposed in Japanese Laid-Open Patent Application No. 58-68016 is not applicable to laser scanning apparatuses using a light source to emit a plurality of laser beams.
In the laser scanning apparatus disclosed in Japanese Laid-Open Patent Application No. 57-54914, a plurality of anamorphic lenses are required to construct the aforesaid afocal anamorphic zoom lens system, and this arrangement disadvantageously necessitates rotational adjustment around the optical axes of said lenses. A minimum of at least three lenses is required to accomplish variable magnification without defocusing, and since said lenses must be individually moved to maintain their respective optical axis, the construction is therefore disadvantageously complicated. Furthermore, the laser beam diameter must be changed to switch resolution, therefore requiring a separate mechanism to change said beam diameter in addition to a mechanism to change the relative position.